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1. Laser Fabrication of Polymeric Microneedles for Transdermal Drug Delivery

   Aldawood, Faisal; Desai, Salil; Andar, Abhay (January 2021, Proceedings of the 2021 IISE Annual Conference)

   null (Ed.)

   Microneedles provide a transdermal pathway for drug delivery, cosmetic infusion, vaccine administration, and disease diagnostics. Microneedle fabrication relies on the interplay of several variables which include design parameters, material properties, and processing conditions. In this research, our group explores the effect of design parameters and process variables for laser ablation of microneedles within a Polymethyl methacrylate (PMMA) mold. An Ytterbium laser (200W) was utilized to study the effect of five inputs factors (laser power, pulse width, number of repetitions, laser waveform, and interval time between laser pulses) on two output factors (diameter and height) of the fabricated microneedles. Polydimethylsiloxane (PDMS) polymer was cast within the PMMA microneedle mold. Scanning electron microscopy (SEM) was employed to image topographical features of the microneedles. Further, mechanical testing of the microneedles was conducted to evaluate the buckling load and deformation behavior of the microneedle array. A 20W pulse laser with trapezoidal waveform resulted in optimal microneedle topography with an aspect ratio of 1.2. ANOVA results (α = 0.05) depicted that laser power and number of repetitions were significant factors determining the geometrical features of the microneedle array. This research establishes a framework for the design and manufacturing of customized microneedles for precision medicine. 

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2. Experimental investigation on nanowire array irradiated with ultrahigh intensity laser at x-ray free electron laser facility SACLA: Fabrication of nanowire array target and its application to ultrafast time-resolved measurements

   https://doi.org/10.1063/5.0251649  

   Tanaka, D.; Sawada, H.; Idesaka, T.; Nakatsuji, C.; Matsuura, S.; Sato, T.; Somekawa, T.; Yabuuchi, T.; Miyanishi, K.; Sueda, K.; et al (March 2025, Journal of Applied Physics)

   Nanowire arrays—vertically aligned metal wires with a few hundred nanometers in diameter—are promising nano-structured targets for high-energy-density physics and related applications. We have been developing ultrafast, time-resolved measurements on laser-irradiated targets using the x-ray free electron laser at the SACLA facility. Here, we present fabrication of various kinds of nanowire array in order to explore the absorption mechanism with ultrahigh intensity laser irradiation, and their application to the laser-irradiation experiment is performed at the SACLA facility. To fabricate nanowire arrays with control over their spatial and material parameters, we have developed an approach using an anodic aluminum oxide template and electroplating processes. The nanowire array samples were applied for ultrahigh intensity laser experiments, which coupled with x-ray free-electron-laser facility SACLA. We characterized fundamental “static” data on transmittance calibration for x-ray shadowgraph measurements. We also evaluated the effect of a pre-pulse on spatial changes of a nanowire, showing that the shape of the nanowires was maintained up to a few picoseconds after laser irradiation. On the preliminary laser-irradiation experiments, we observed time-resolved, two-dimensional x-ray images and observed the x-ray transmittance change due to the heating process. 

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3. An efficient 2D array of blue-detuned optical traps

   Graham, Trent; Xiaoyu, Jiang; Poole, Cody; Sun, Yuan; Lichtman, Martin; Saffman, Mark (May 2018, Bulletin American Physical Society, DAMOP 2018)

   We demonstrate a 2D lattice of blue-detuned optical traps which uses laser power efficiently, is tolerant to perturbations in beam alignment, and is insensitive to interferometric phases. Blue traps have several advantages over red traps despite requir- ing a more complicated beam geometry. Since atoms in a blue trap sit at an intensity minimum, Stark shift noise and site-to-site calibrations are minimized. However, constructing a blue lattice which efficiently con- verts laser power into trap depth, is challenging. For example, a lattice of bottle beams is inefficient because neighboring sites are separated by two walls, limiting the number of traps that can be formed. An array of tightly spaced Gaussian beams is a more efficient blue trap, but the trap potentials are susceptible to alignment perturbations. We demonstrate an array which uses diffractive optical elements to create a cross-hatched pattern of lines in the focal region where the atoms are trapped in up to 121 sites. This "line array" is almost twice as efficient as the Gaussian beam array and is more resilient to perturbations in beam alignment. 

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4. Lasing from InP Nanowire Photonic Crystals on InP Substrate

   https://doi.org/10.1002/adom.202001745  

   Tu, Chia‐Wei; Fränzl, Martin; Gao, Qian; Tan, Hark‐Hoe; Jagadish, Chennupati; Schmitzer, Heidrun; Wagner, Hans_Peter (December 2020, Advanced Optical Materials)

   Abstract 2D photonic crystal (PhC) lasing from an InP nanowire array still attached to the InP substrate is demonstrated for the first time. The undoped wurtzite InP nanowire array is grown by selective area epitaxy and coated with a 10 nm thick Al₂O₃film to suppress atmospheric oxidation and band‐bending effects. The PhC array displays optically pumped lasing at room temperature at a pulsed threshold fluence of 14 µJ cm⁻². At liquid nitrogen temperature, the array shows lasing under continuous wave excitation at a threshold intensity of 500 W cm⁻². The output power of the single mode laser line reaches values of 470 µW. Rate equation calculations indicate a quality factor ofQ ≈ 1000. Investigations near threshold reveal that lasing starts from isolated islands within the pumped region before coherently merging into a single homogeneous area with increasing excitation power. This field emits a lasing mode with an average off‐normal angle of ≈6°. Single mode lasing with the nanoarray still attached to the InP substrate opens new design opportunities for electrically pumped PhC laser light sources. 

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5. Polarization-Controlled Microchannel Arrays Induced by Femtosecond Laser Pulses

   Garcell, E; Guo, C. (April 2018, Journal of applied physics)

   Using pulsed femtosecond laser irradiation, we demonstrate the creation of an array of microgrooves within a single laser spot on metals. The orientation of these grooves is not limited to being parallel to the plane of the laser beam’s propagation but can orient at any angle up to 30 degree from parallel. We control the orientation of the microgrooves by proportionally varying the laser’s polarization. Polarization, angle of incidence, and structural evolution dynamics have been thoroughly studied to help us understand this phenomenon. Our studies suggest that the formation of angled microgroove arrays is due to a feedback effect occurring between defect-focused ablation and polarization-dependent laser-induced periodic surface structures. 

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